Photosensitive control circuit



y 1963 B. STEIN, JR., ETAI. 3,091,723

PHOTOSENSITIVE CONTROL CIRCUIT Filed June 5, 1961 Line Load Neutral INVENTORS. I Laurence. BSfeinJr. v

' Robert C.Mc Donald ATTORNEYS.

nited rates This invention relates to control devices and particularly to an improved photoelectric device for automatically controlling a load according to ambient light or other conditions and includes temporary manual controls with provision for automatic rearming.

A previous device of this nature was described in patent application No. 21,291, filed in the name of Philip Garnick et al., and assigned to the same assignee as the instant application. The present device represents an improvement over the prior one in that the photocell is now in a parallel path rather than in series with one relay and thus controls either the load connecting relay or the manual override relay. In addition, whereas both relays formerly had to be large in order for either to control the load con nection, now only one large relay is utilized for that purpose, while the other only switches the coil of the first relay. A further manual control is provided to maintain the load, such as a lamp, in an energized condition during the day as well as at night.

It is therefore the primary object of the present invention to provide an improved and simplified photoelectric circuit for automatically controlling a load, including a temporary manual override switch for use during darkness which resets automatically at daylight and a second manual switch to permit operation of the load during the day.

The invention will be more fully understood and other objects and advantages will become apparent in the following description and accompanying drawing, in which:

The FIGURE is a circuit diagram of one embodiment of the invention.

As shown in the drawing, the circuit is connected by lines and 12 through terminals 14 and 16 to an alternating current supply. A load, such as a group of lamps, is connected directly to terminal 16, and to terminal 10 by way of terminal 18 and a normally open relay contact 20 of relay I. A series resistor 22 connects line 12 to one side of relay I and the other side connects to line 10 through a normally closed contact 24 of relay II. The latter relay is also connected to resistor 22 in a path parallel to relay I and is in series with a normally closed momentary acting manually operated push button switch 26 and a normally open contact 28 of relay II, which connects to line 10. A second normally open manual switch 30 is connected between switch 26 and line 10 to bypass contact 28. Photocell 32 is connected in a third parallel path between resistor 22 and line 10 and includes a normally closed sustained action manual switch 34 in series with the photocell. A fourth parallel path including a resistor 36 and normally closed contact 38 of relay I also connects between resistor 22 and line 10.

During daylight conditions, the resistance of photocell 32 is very low, thereby shunting most of the current around the closed parallel paths, including that of relay coil I, to prevent the relay from energizing. As the light level decreases toward darkness, the resistance of the cell increases, permitting more current to flow through relay I, until it energizes at a predetermined level and closes the load contact 20 to turn on the lights.

Resistors 36 and 22 during this time form a voltage divider across the line, with resistor 36 shunting the photocell and relay I. When relay I energizes, it opens contact 38 and removes resistor 36 from the circuit. This action permits still more current to flow through relay I and aids in making the operation more positive. When the situation is later reversed, resistor 36 is placed back in circuit by closing of contact 38, with the resistor aiding the relay to de-energize in a positive manner. The action is equivalent to positive current feedback with respect to the coil of relay I.

Resistor 22 serves to limit the current in the circuit and is necessary due to the low resistance of the photocell in bright light. Resistor 22 also provides an impedance which permits the voltage across the relay coils to vary as the resistance of the cell varies and in combination with resistor 36 determines the exact operating point of the relays.

The swamping efiect of resistor 36 and the relay coil in parallel with the cell tend to make the circuit less critical with regard to the cell sensitivity. However, where more critical operation is desired, resistors 36 and 22 and the relays can be adjusted to provide finer control of the turn-on and turn-oft points.

Switches 26 and 30 are momentary acting manually operated pushbuttons which control relay II in opening and closing the load circuit during darkness. When normally open switch 30 is operated, the open contact 28 of relay II is bypassed, causing relay II to be energized. This action closes contact 28 to maintain a complete path for relay II after switch 30 returns to an open position.

The operation of relay II opens the normally closed contact 24 in series with relay I and tie-energizes the latter, to cause contact 20 to open the load connection. Relay II remains energized until normally closed switch 26 is opened. This action opens the circuit of relay II and closes that of relay I to return the load to the On condition. If switch 26 is not operated, relay II remains actuated and the load remains Off until the following day, when the photocell will again shunt the current to cause relay II to drop out and return the circuit to the original condition. Thus, the circuit is automatically rearmed or reset for the following evening when darkness will again cause the lights to be turned On.

Switch 34 is a sustained action normally closed manually operated pushbutton which permits the light to be turned On during the day, or continuously, if so desired. This feature is particularly useful for advertising displays or other similar applications. Opening switch 34 has the same effect as darkness and removes the shunting effect of the photocell to permit relay I to close the load connection. The circuit can then be returned to automatic operation by depressing switch 26 or 30 which are mechanically connected to switch 34-, as shown by dot and dash lines 40, to release the latter switch and return it to a closed position. Thus, the cell is again placed in the circuit to regain control.

Any suitable switch construction may be utilized and the mechanical connections between the switches may be of any character adapted to perform the functions stated. An example of a satisfactory construction which may be utilized is a three position switch made by Ark-Les Switch Corporation.

Due to the tendency of the photocell sensitivity to decrease with age and require higher light levels for operation, the load would be turned ON earlier and OFF later. This condition may be compensated for by adjustment of the various elements. Another important feature of the invention results from the fact that the load is always switched by relay I. Therefore, the manual override relay II, which switches only the coil of the load relay, may be small and constructed of light material while only relay I need 'be of a heavy construction. The added manual control for connecting the load during daylight is a further novel feature of the present invention.

In its broader aspects the present invention is applicable to use with control elements responsive to changes in external physical phenomena other than light. Other control elements may be utilized in place of the relay and photocell. For example, heat sensitive thermistors or voltage sensitive devices can be employed, which also change resistance in accordance with the magnitude of energy applied.

The present construction provides an improved, simplified control circuit having both automatic and manual controls which may be employed in a variety of applications. While only a single embodiment has been illustrated, it is apparent that the invention is not limited to the exact form or use shown and that many variations may be made in the particular design and configuration without departing from the scope of the invention as set forth in the appended claims.

What is claimed is:

1. A control device comprising current supply means having a pair of terminals, load means connected to one said terminal, first switch means in series with said load to connect and disconnect said load to said other terminal, first control means connected between said terminals and adapted to operate said first switch means, variable resistance means connected in parallel with said first control means and having a resistance which varies in accordance with some external physical phenomenon, said variable resistance means adapted to automatically energize and de-energize said first control means in accordance with predetermined conditions of said physical phenomenon, second switch means in series with said first control means to connect and disconnect said first control means between said terminals, second control means in parallel with said first control means and adapted to operate said second switch means, first manual switch means in series with and adapted to energize and deenergize said second control means, said resistance means adapted to automatically de-energize said second control means upon the occurrence of a predetermined condition of said resistance.

2. The device of claim 1, in which the variable resistance means is a photocell.

3. The device of claim 1, including second manual switch means in series with and adapted to disconnect said variable resistance means to cause said first control means to energize and hold said lead in continuous connection with said other terminal, said first manual switch means being mechanically connected to said second manual switch means to permit release thereof and to reconnect said resistance means for automatic operation.

4. The device of claim 3, including voltage divider means connected between said terminals, one portion of said divider being in parallel with each said control and variable resistance means and another portion being in series therewith, said parallel portion including switch means actuated by said first control means to disconnect and connect said parallel portion to permit positive energizing and tie-energizing of said first control means at said predetermined conditions.

5. The device of claim 3, wherein said control means comprise relays, said switch means controlled thereby comprise relay contacts and said variable resistance means comprises a photocell.

6. The device of claim 5, wherein the resistance of said photocell increases with decreasing light conditions to cause an increased current to energize said first control means at a predetermined light conditiog, said first control means closing said first switch means to connect said load.

7. The device of claim 3, wherein said first switch means in series with said load comprises a first normally open contact, said second switch means comprises a first normally closed contact in series with said first relay control means, said first relay being energized at said predetermined condition to close said first open contact means and connect said load, said manual switch means comprises a first normally closed momentary manual switch and a second normally open relay contact, a normally open manual switch in parallel with said second normally open relay contact and in series with said first normally closed manual switch, said second manual switch adapted to connect and energize said second relay control means to close said second normally open contact and open said first normally closed contact to deenergize said first relay and open said load connection, said first manual switch being adapted to open said connection of said second relay and reconnect said first relay and said load, and wherein said second manual switch means includes a normally closed sustained action switch and said parallel voltage divider portion switch means comprises a normally closed contact.

Cassidy July 14, 1953 De Magondeaux Nov. 11, 1958 

1. A CONTROL DEVICE COMPRISING CURRENT SUPPLY MEANS HAVING A PAIR OF TERMINALS, LOAD MEANS CONNECTED TO ONE SAID TERMINAL, FIRST SWITCH MEANS IN SERIES WITH SAID LOAD TO CONNECT AND DISCONNECT SAID LOAD TO SAID OTHER TERMINAL, FIRST CONTROL MEANS CONNECTED BETWEEN SAID TERMINALS AND ADAPTED TO OPERATE SAID FIRST SWITCH MEANS, VARIABLE RESISTANCE MEANS CONNECTED IN PARALLEL WITH SAID FIRST CONTROL MEANS AND HAVING A RESISTANCE WHICH VARIES IN ACCORDANCE WITH SOME EXTERNAL PHYSICAL PHENOMENON, SAID VARIABLE RESISTANCE MEANS ADAPTED TO AUTOMATICALLY ENERGIZE AND DE-ENERGIZE SAID FIRST CONTROL MEANS IN ACCORDANCE WITH PREDETERMINED CONDITIONS OF SAID PHYSICAL 